Monday, September 24, 2012

Dry finish to a dry month.. 2nd driest September on record possible

September 2012 will be ending on a sunny and dry note over the Red River valley and southern Manitoba.. a fitting end to what has been an exceptionally dry month. As of today, only 4 mm of rain has fallen at Winnipeg airport this month, with no precipitation forecast all this week through the end of the month. If so, September will end up as the 2nd driest September on record in Winnipeg since records began 140 years ago in 1872. Only September 1948 will have been drier in the city at 1.3 mm for the month.

Rainfall past 30 days across Prairies. Note large area with little or no rain over the past month.

Normal September rainfall is around 52 mm, so this month's rainfall has been less than 10% of normal. The last appreciable rainfall in Winnipeg was back on August 15th when 9 mm was recorded. Since then, only about 5 mm of rain has fallen in the past 6 weeks, coming off a dry summer that saw a little more than half our normal summer rainfall. This is resulting in very low soil moisture levels, with cracking and shifting clay causing problems with city watermains and house foundations. The dry soil conditions will also become an increasing concern for agriculture and forestry interests if adequate moisture is not received over the winter months. Why has it been so dry? Simply put, the jet stream has been steering storm systems away from the southern Prairies over the past month, with storms systems tracking mainly across northern regions. This has been mainly due to a persistent upper ridge over western Canada that has effectively blocked moisture laden systems off the Pacific from tracking across the southern Prairies (see image of rainfall over past 30 days across Prairies) A pattern change will be needed in October to bring some precipitation bearing systems across southern Manitoba, but past history suggests that may not happen. Of the top 5 driest Septembers in Winnipeg, all but one were followed by much drier than normal Octobers.

13 comments:

Manitoba has been on the western edge of a large upper trof over central canada over the last week and a half or so with that upper ridge to the west of us, which would explain the cooler conditions we've been seeing off and on since we're on the western edge of the core of the trof (jet streak). Problem is we're in the entrance region of the jet streak where there is strong convergence occurring with all that air piling up as it enters the jet streak, allowing cold air to sink to the surface and give dry conditions under the area of convergence (cool and dry), other than some lake enhanced stuff we've been seeing with that northerly flow picking moisture up off the lakes. This has almost seemed like a stalled pattern over the last while and for someone who appreciates rainy days, such as myself, are hoping the jet stream pattern changes soon.

Yeah, a bogus 0.5 mm reading from YWG airport, and it wasn't even windy (when a lot of these bogus 0.5 mm reports are generated) May have been due to some of that freezing fog in the morning. Regardless, it wasn't an actual precip amount and should be removed. Note that a colocated EC gauge (XWG) didn't record any precip yesterday, and has only 2.9 mm for the month.

Long range models pointing to colder than normal weather returning next week, with single digit highs possible by mid week. EC's current ensemble forecast for day 6-7 not catching cool outbreak at this point showing highs in the mid teens. Look for those numbers to come down significantly over the next couple of days based on current long range indicators..

Robbed of a beautiful day today over Winnipeg and northern RRV with this pesky band of mid level cloud over us, likely associated with warm front. Hopefully we see some sun this afternoon, but nicer day to our south with plenty of sun and warmer temps.

Looking at the type of pattern setting up and CPC's outlooks, I would say this next cooldown looks to be be more prolonged, perhaps 1-2 weeks. There is a slightly better chance of seeing some precip with this cooler weather pattern, but overall it still looks drier than normal in the short term. Latest drought statement from US shows areas of severe drought has expanded in portions of eastern ND and NW Minnesota.

Looks like they removed yesterday's 0.5 mm phantom precip reading from YWG stats. Back to 4.0 mm for the month. Looks like they're being more proactive on these suspicious obs which is good to see.

Note also that we're at an average monthly temperature of 12.3C for September at YWG airport, which is exactly normal (by 1971-2000 standards). We have 3 more above normal days coming up that will likely get that average up a couple tenths, and keep our above normal streak alive at 15 straight months. Amazing.

Beautiful day on tap Saturday with temperatures getting up to 27C in Winnipeg.. NAM even hinting at a possible 30C but that seems a bit optimistic. Regardless, this will likely be the last time this season we see temperatures in the upper 20s, with colder than normal weather moving in for the first part of October. Enjoy it while it lasts!